Illustrated herein are embodiments for adjusting output characteristics, such as image quality, uniformity and consistency, in printing systems. Embodiments will be described with specific reference to systems having multiple xerographic or electrophotographic marking engines. However, it is to be understood that the embodiments are capable of broad use in association with a wide variety of printing or other rendering systems and technologies, and that such use is contemplated herein.
Printing systems have been developed that include multiple marking engines which are interconnected between a media supply and a media output by a plurality of pathways. Exemplary systems are shown in one or more of the below cross-referenced applications, such as U.S. application Ser. Nos. 10/917,768; 10/924,106; 10/924,459; and 11/051,817, for example. Such systems provide numerous benefits and advantages over other known printing systems, including increased performance or output rates and improved reliability. These benefits and advantages can be at least partly attributed to the ability of these systems to use multiple marking engines in the production of any one document. Said differently, these systems are capable of printing some pages or sides of sheets of a document using one marking engine and other pages or sides of sheets using one or more other, different marking engines. Thus, advantages in performance and reliability can be attained.
It will be recognized, though, that it is desirable for the documents produced by such multi-engine marking systems to maintain the high level of document quality, and image uniformity and consistency expected of other printing and/or marking systems. Additionally, it will be recognized that each marking engine operates within a nominal operating window that includes many factors and variables, which in turn influence the images output by the marking engine. As such, it could be possible for two or more marking engines to each be operable within the established operating window for that respective marking engine and yet produce printed images having observably different image qualities and characteristics when the printed images are compared side-by-side. For example, it would be undesirable to produce a document having sheets with different appearances, and could be particularly problematic where the pages are adjacent one another, such as on facing pages of a document printed in duplex.
An observably different appearance from one page or sheet to the next can result from even minor variations in image qualities and characteristics such as, but not limited to, overall image lightness, overall image darkness, image contrast, image line weight, shadow detail, solid area differences and a wide variety of other image conditions. Most image qualities and characteristics are attributable to or can be otherwise associated with specific operating conditions or actuator settings of a marking engine. By adjusting one or more of the operating conditions, actuator settings and/or other parameters of the specific marking engine, it is often possible to adjust one or more of the corresponding output conditions toward an optimal or otherwise predetermined setpoint.
In systems having multiple marking engines it is usually possible to use regular process controls to adjust at least some engine conditions and parameters. This helps to maintain the output and operation of each printing or marking engine within its nominal operating window. Additionally, systems have been developed that are operable to minimize overall system variability by coordinating the adjustments made to the operating conditions, actuator settings and/or other parameters of multiple engines toward optimal or otherwise predetermined setpoints. Thus, each engine is adjusted to be within its own output specification and also toward coordinated setpoints to thereby generate an improved overall system response. Exemplary systems are disclosed in one or more of the below cross-referenced applications, such as U.S. application Ser. No. 10/999,326 (the '326 application), for example.
It will be appreciated, however, that due to the number of actuators, conditions (both static and dynamic) and other variables, it is generally not practical to provide for adjustment of a large number of image characteristics and output conditions. Providing for such a large number of adjustments would likely significantly increase the number of components and the overall complexity of the system, as well as the attendant increase in costs associated therewith. Thus, systems are normally developed that are adapted to monitor and/or adjust those engine conditions, actuators and/or parameters that tend to have a more significant impact on engine outputs, such as quality or consistency, or that tend to fall out of adjustment more frequently. Image qualities and output conditions due to or associated with other unmonitored engine conditions are often left to be accommodated for by the regular process controls.
As an example, the cleaning field boundary is normally associated with output conditions such as line width. Applicant has recognized that marking engines running at different cleaning field boundaries could output images having different highlight density, and that such an occurrence could undesirably result in images having observably different appearances. As discussed above, such a variation in output conditions could be particularly problematic where different pages or sheets of a single document are produced by different marking engines of a multiple marking engine system. To date, however, the regular process controls of printing systems having multiple marking engines have not been adapted to include cleaning field boundary adjustments. Thus, any variations in image quality and/or output characteristics that can be attributed to differences in the cleaning field boundaries of the multiple marking engines have been left to be resolved by the regular process controls without performing any adjustment to the cleaning field boundaries. This, however, tends to cause the regular process controls to operate at or near the limits for making such corrections and adjustments.
In printing systems having a single marking engine, regular process controls can be used to adjust engine conditions and parameters, including the cleaning field boundary. However, a densitometer, such as a black toner area coverage (BTAC) sensor, or other suitable hardware is normally used in association with an attendant control loop to perform adjustments to the cleaning field. Using these and/or other sensors and the associated control loops is an effective approach to adjusting the cleaning field of a marking engine. However, these sensors and associated controls are undesirably associated with increased physical space requirements, system complexity, and production and maintenance costs. Implementing such an arrangement in printing systems having multiple marking engines is generally undesirable as this further increases these factors. That is, additional print engines would utilize more sensor hardware and wiring as each print engine should include its own sensors. This would tend to undesirably increase system complexity and the overall costs associated therewith.